One or more embodiments of the present invention pertains to method and apparatus for measuring a corneal profile of an eye. In particular, one or more embodiments of the present invention relates to method and apparatus for measuring a corneal topography and a corneal thickness profile of an eye.
Accurate measurement of a corneal topography and a corneal thickness profile is important for the safety and effectiveness of corneal refractive surgery. As is well known, the corneal topography (for example, curvature (slope) and elevation profiles) of an anterior surface of a cornea, can be provided by a corneal topographer. Further, it is also well known how to use ray-tracing algorithms to combine slit light beam images and the corneal topography to measure the corneal thickness profile.
For example, whenever a slit light beam is projected onto the cornea, and a cross section of the slit light beam on the cornea is viewed from an angle, the corneal thickness profile can be observed and analyzed. Further, if the projection angle and the viewing angle of the slit light beam are predetermined, and the corneal topography is measured, the corneal thickness profile of the cornea can be calculated from the measured width of the cross section of the intersection of the slit light beam on the cornea.
As disclosed in U.S. Pat. Nos. 5,512,965 and 5,512,966 (inventor Richard K. Snook, the xe2x80x9cSnookxe2x80x9d patents), slit light beam images are recorded by a video camera, and the recorded images are processed in a digital format to produce a corneal curvature profile and a corneal thickness profile. As disclosed, slit light beams are projected from two sides of an instrument axis, and slit light beam images are taken along the instrument axis. During the disclosed measurement procedure, the slit light beams are scanned across the cornea in a parallel direction, and a video image is taken at each step of the slit light beam scan positions. To obtain an accurate measurement of the corneal thickness profile, one needs an accurate measurement of the corneal topography with high spatial resolution. This, in turn, requires the corneal topography to be measured at a large number of points across the anterior surface of the cornea. Thus, as disclosed, a large number of slit light beam images are required to generate sufficient data to measure accurately the corneal topography and the corneal thickness profile. In practice, a commercial instrument based on the disclosed design principle takes some forty (40) images for each measurement, and as a result, the data acquisition process takes more than one second to complete.
In U.S. Pat. Nos. 6,079,831, 6,120,150, and 6,257,723 (inventors Edwin J. Sarver and Charles R. Broadus, the xe2x80x9cSarver et al.xe2x80x9d patents), device and method are disclosed for mapping a corneal topography of an eye using elevation measurements in combination with slope measurements. For example, in accordance with one method disclosed therein, elevation measurements of the eye are collected using a slit beam diffuse reflection system, such as an ORBSCAN(trademark) device. An approximating b-spline surface is then fitted to the elevation measurements. Slope measurements of the eye are collected using a Placido-based reflective system, but the slope measurements are referenced to points on the b-spline surface. The elevation and slope measurements are then blended using weighted least squares fitting techniques. Finally, a new b-spline surface is fitted to the blended measurements. However, it would be desirable to improve on the accuracy of the corneal topography provided as taught in the Sarver et al. patents.
In light of the above, there is a need in the art for method and apparatus for measuring corneal profiles of an eye that can operate quickly with improved accuracy.
One or more embodiments of the present invention advantageously satisfy one or more of the above-identified needs in the art. Specifically, one embodiment of the present invention is a corneal diagnostic instrument that determines a corneal topography and a corneal thickness profile. In particular, one embodiment of the present invention comprises: (a) a Placido ring illuminator disposed to project a Placido ring image onto a cornea to generate a reflected Placido ring image; (b) multiple slit lamp projectors disposed to project slit light beams onto the cornea to generate slit light beam images; (c) a camera system optically disposed to detect the reflected Placido ring image and the slit light beam images; and (d) a controller, coupled to the slit lamp projectors, the Placido ring illuminator, and the camera system, to cause the slit light beam images and the reflected Placido ring image to be generated and detected in a predetermined sequence, wherein the controller is responsive to the detected reflected Placido ring image and the detected slit light beam images to determine a corneal thickness profile.
Another embodiment of the present invention is a corneal diagnostic instrument that comprises: (a) a corneal topographer that determines a corneal topography of an anterior surface of a cornea; (b) multiple slit lamp projectors disposed to project slit light beams onto the cornea to generate slit light beam images; (c) a camera system optically disposed to detect the slit light beam images; and (d) a controller, coupled to the slit lamp projectors, the corneal topographer, and the camera system, to cause, in a predetermined sequence, (i) the slit light beam images to be generated and detected, and (ii) the corneal topographer to obtain data used to determine the corneal topography, wherein the controller is responsive to the corneal topography and to the detected slit light beam images output from the camera to determine a corneal thickness profile.